1. Field of the Invention
This invention relates to an improvement in a reduction gearing device of a windshield wiper motor suitable for use in an electric windshield wiper provided with a stop-position controlling system, which wipes raindrops or the like from a windshield glass of an automotive vehicle so as not to obstruct the driving of the vehicle and stops a wiper blade to a predetermined position after the wiping.
2. Description of the Prior Art
As the conventional reduction gearing device of the wiper motor, there is a structure as shown in FIGS. 1 and 2. Further, the conventional stop-position controlling system is a structure as shown in FIG. 3.
Particularly, FIG. 1 shows a state of removing a cover from the gearing mechanical portion of the wiper motor, while FIG. 2 shows a partial section of the gearing mechanical portion of the wiper motor.
In FIGS. 1 and 2, numeral 1 is a motor for driving a wiper of a vehicle, numeral 2 is a gear housing connected to a housing of the motor 1, and numeral 3 is a cover for the gear housing 2. The turning force of the motor 1 is transmitted to a worm shaft 4 extending from a motor shaft of the motor 1. The worm shaft 4 is provided with right-threaded worm at one end side and left-threaded worm at the other end side. These worms are in engage with large-size gear members 5a, 6a in two-stage intermediate gears 5, 6 mounted in the gear housing 2, respectively. In this case, the intermediate gears 5, 6 are arranged at opposite sides on the worm shaft 4 so as to turn them in the same direction. Further, small-size gear members 5b, 6b of the intermediate gears 5, 6 are in engage with an output gear 7b pivotably supported through a metal bearing 7a in the gear housing 2. Thus, a rotary shaft of the output gear 7b is an output shaft 7c for the transmission of rotations.
In the reduction gearing device of the above structure, the right-threaded worm and left-threaded worm are provided on the worm shaft 4 and are in engage with the intermediate gears 5, 6 engaging with the output gear 7, whereby radial loadings produced in the worms due to the rotation of the worm shaft 4 are substantially offset with each other and also thrust loading in axial direction can completely be restrained. Therefore, this reduction gearing device becomes a gearing mechanism mitigating a transmission loss of rotation in high efficiencey.
There will be described the stop-position controlling system as shown in FIG. 3 below.
In FIG. 3, numeral 7b is the output gear as described above and is provided with a first contact plate 8 of a disc shape having a folding fan-shaped notch portion and a second contact plate 9 disposed at a position corresponding to the notch portion apart from the first contact plate 8 and protruded outward from the first contact plate 8. With respect to the output gear 7b, as shown in FIG. 2, the cover 3 of gear housing 2 is provided with a first contactor 12, which is connected between the motor 1 and breaker 11 connecting at one end to a power source 10 and protecting the motor during the locking thereof and is capable of coming into contact with only the second contact plate 9, and a second contactor 14 connected to an off-terminal 13 and being capable of coming into contact with both the first and second contact plates 8 and 9, whereby the first contactor 12 becomes connected to the second contactor 14 through the second contact plate 9 every one rotation of the output gear 7b. Moreover, a wiper blade (not shown) performs one reciprocating movement every one rotation of the output gear 7b. Particularly, when the contactors 12, 14 are connected to each other through the second contact plate 9, the wiper blade arrives at a wipe-finishing position. In FIG. 3, numeral 15 is an earth terminal of a control switch, numeral 16 is a high-speed operating terminal, numeral 17 is a low-speed operating terminal, and numeral 18 is a movable contact connected to a wiper switch.
When the wiper switch is randomly turned off during the operation of the wiper provided with the stop position controlling system of the above structure, the movable contact 18 renders the off-terminal 13 and the low-speed operating terminal 17 into the contact state. In this case, the operation of the wiper is still continued because electric current flows through the contacting of the second contactor 14 with the first rotating contact plate 8. However, when the second contactor 14 is separated from the first contact plate 8, electric current to the motor 1 is shut off. Thereafter, the second contactor 14 and the first contactor 12 arc rendered into contact state through the second contact plate 9, whereby the connection to the earth side of the power source 10 is released to form a short-circuit of the motor 1, resulting in the braking of the wiper operation. Thus, the wiper blade can always be stopped at a wipe-finishing position.
In the conventional reduction gearing device of the windshield wiper motor provided with the stop position controlling system as mentioned above, however, when the movement of the wiper blade is stopped by the weight of the lying snow in a snowy day of winter season, the breaker 11 actuates for the protection of the motor to shut off electric current, whereby the rotation of the motor 1 is forcedly stopped from exterior, which causes the reverse rotation as a reaction. In this case, since the reduction gearing device connected to the motor 1 is high in the efficiency, the reverse rotation of the motor is transmitted to the reduction gearing device to apply impact torque to each gear in the gearing mechanism, resulting in the damaging of the gear. Further, when the wiper switch is intermittently switched on-off during snowfall, snow may be lain near the wipe-finishing position, so that even if the wiper switch is turned off, the wiper blade is not stopped to the normal wipe finishing position. In this case, when the wiper blade is forcedly stopped between the first contact plate 8 and the second contact plate 9, electric current is shut off, but the motor 1 causes reverse rotation as a reaction of the stopping of the wiper blade, whereby the second contactor 14 may slightly contact with the first contact plate 8 to cause sparking. Then, such a sparking turns on electricity, but the wiper blade is forcedly stopped to a position apart from the normal stop-position by the lying snow, so that the motor 1 is locked and the breaker 11 actuates to shut off electric current. However, the breaker 11 is rapidly released to turn on electric current, but the wiper blade still stops forcedly, so that the above mentioned sparking is repeated. Therefore, when the output gear 7a is made from a synthetic resin, it is melted out by the heat of repeated sparks, so that the second contactor 14 enters into the molten portion of the output gear 7a to produce troubles such as unsatisfactorily automatic stopping of the wiper blade and the like.